1. Field of the Invention
The present invention relates to a magnetic sensing element including a pinned magnetic layer, in which the magnetization direction is pinned in one direction, and a free magnetic layer disposed on the above-described pinned magnetic layer with a non-magnetic material layer therebetween. In particular, it relates to a magnetic sensing element capable of stabilizing a reproduction output.
2. Description of the Related Art
FIG. 9 is a partial sectional view of a known magnetic sensing element (spin-valve type thin film element) cut from a direction parallel to a surface facing a recording medium.
Reference numeral 1 shown in FIG. 9 denotes a substrate layer made of Ta, and a seed layer 2 made of NiFeCr or the like is disposed on the substrate layer 1.
A multilayer film T, in which an antiferromagnetic layer 3, a pinned magnetic layer 4, a non-magnetic material layer 5, a free magnetic layer 6, and a protective layer 7 are laminated sequentially, is disposed on the seed layer 2.
The free magnetic layer 6 and the pinned magnetic layer 4 are formed from a Heusler alloy, e.g., Co2MnGe. The non-magnetic material layer 5 is formed from Cu. The antiferromagnetic layer 3 is formed from PtMn. The protective layer 7 is formed from Ta.
An exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer 3 and the pinned magnetic layer 4 and, thereby, the magnetization of the above-described pinned magnetic layer 4 is pinned in a height direction (Y direction shown in the drawing).
Hard bias layers 8 made of a hard magnetic material, e.g., CoPt, are disposed on both sides of the free magnetic layer 6. The top, the bottom, and the end portions of the hard bias layer 8 are insulated by an insulating layer 9. The magnetization of the free magnetic layer 6 is aligned in a track-width direction (X direction shown in the drawing) by longitudinal bias magnetic fields from the hard bias layers 8. Electrode layers 10 and 10 are disposed on and under the multilayer film T.
When an external magnetic field is applied to the magnetic sensing element shown in FIG. 9, the magnetization direction of the free magnetic layer is varied relatively to the magnetization direction of the pinned magnetic layer and, thereby, the resistance value of the multilayer film is varied. In the case where a sensing current of a constant current value is passed, the external magnetic field can be detected by detecting this change in resistance value as a change in voltage.
A magnetic sensing element including a pinned magnetic layer made of a Heusler alloy is described in Japanese Unexamined Patent Application Publication No. 2003-309305 (page 8, FIG. 4).
FIG. 10 is a magnified partial schematic diagram of the structure of the magnetic sensing element shown in FIG. 9. It is difficult to completely flatten the surface of the pinned magnetic layer 4 and, usually, minute waves are generated on the surface. If the waves are generated on the surface of the pinned magnetic layer 4, analogous waves are generated on the surfaces of the non-magnetic material layer 5 and the free magnetic layer 6.
When such a wave is generated, as shown in FIG. 10 (a schematic diagram showing cross sections of the pinned magnetic layer 4, the non-magnetic material layer 5, and the free magnetic layer 6 shown in FIG. 9, cut in the Y direction), magnetic poles are generated at the wave portion on the surface of the pinned magnetic layer 4. The above-described magnetic poles are also generated at the wave portion on the free magnetic layer 6 facing the pinned magnetic layer 4 with the non-magnetic material layer 5 therebetween. Consequently, the ferromagnetic coupling magnetic field Hin due to the magnetostatic coupling (topological coupling) between the pinned magnetic layer 4 and the free magnetic layer 6 is enhanced. Therefore, the free magnetic layer 6, which must be magnetized essentially in the X direction shown in the drawing, is subjected to the action to magnetize in the Y direction shown in the drawing, and a problem occurs in that the asymmetry of the reproduction waveform is increased when an external magnetic field is applied in a direction different by 180 degrees.